Examples:

Today many people complain about nose bleeding. Nose bleeding is often attributable to a very simple cause. On the whole we live today in overheated rooms with dry air. Air conditioning systems aggravate this effect. It is right at the beginning of the respiratory system, i.e. in the front sections of the nose, that the mucous membrane dries out upon inhalation of this dry air and is thus becomes prone to laceration and then bleeding. The mucous membrane is often overtaxed with its task to moisten the air.

Anyone who has ever cleaned out a dusty attic or cellar knows how well the nose is able to perform the task of cleaning. If one blows one's nose after finishing work, then a lot of dirt will be found in the handkerchief. If the same person coughs up a bit of phlegm from the bronchi, then hardly any dirt will be found in it. The nose has been able to clean the air almost completely.

The rougher (larger) the particles in the air, the sooner the particles are trapped. On the other hand, the smaller the particles, the deeper they penetrate into the respiratory system and, in extreme cases, all the way down to the ends of the respiratory system - into the alveoli.

This well-working "air conditioning system" is switched off by anyone who inhales air through the mouth. Air that is too cold, too warm, too dry or air that contains too many dust particles puts a particular burden on deeper respiratory passages. Short phases in which breathing is carried out via the mouth are unquestionably harmless. However, improper and inordinate stress for too long a period of time can result in damage to the respiratory system and resulting illness.

Think about workers who perform their work in dusty air, e.g. miners, carpenters or even bakers. They are required to wear a mask because of the health hazard.

Or think about professional athletes who breathe through the mouth in order to be able to breathe in and out as much air as possible as quickly as possible. Many of these athletes suffer from illnesses of the respiratory system.